# Auger effect

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{{short description|Physical phenomenon}}
[[File:Auger Process.svg|thumb|340px|Two views of the Auger process using the [Bohr model](/source/Bohr_model) of the atom. (a) illustrates sequentially the steps involved in Auger deexcitation. An incident electron (or photon) creates a core hole in the 1s level. An electron from the 2s level fills in the 1s hole, and the transition energy is imparted to a 2p electron, which is emitted. The final atomic state thus has two holes, one in the 2s orbital and the other in the 2p orbital. (b) illustrates the same process using [X-ray notation](/source/X-ray_notation), KL<sub alt="KL_1L_{2,3}">1</sub>L<sub>2,3</sub>.]]
The '''Meitner–Auger effect''' is a physical phenomenon in which [atom](/source/atom)s eject [electrons](/source/electrons). It occurs when an [inner-shell](/source/inner-shell_electrons) vacancy in an [atom](/source/atom) is filled by an electron, releasing energy that causes the emission of another electron from a different shell of the same atom.<ref>{{GoldBookRef|title=Auger effect|file=A00520}}</ref>

When a [core electron](/source/core_electron) is removed, leaving a vacancy, an electron from a higher energy level may fall into the vacancy, resulting in a release of [energy](/source/energy). For light atoms (Z<12), this energy is most often transferred to a valence electron which is subsequently ejected from the atom.<ref name="Photoabsorption">{{cite book |last1=Berkowitz |title=Photoabsorption, Photoionization, and Photoelectron Spectroscopy |publisher=Academic Press |isbn=978-0-12-091650-4 |page=156 |doi=10.1016/B978-0-12-091650-4.50011-6 }}</ref> This second ejected electron is called an '''Auger electron'''.<ref>{{GoldBookRef|title=Auger electron|file=A00521}}</ref> For heavier atomic nuclei, the release of the energy in the form of an emitted [photon](/source/photon) becomes gradually more probable.

==Effect==
Upon ejection, the [kinetic energy](/source/kinetic_energy) of the Auger electron corresponds to the difference between the energy of the initial [electronic transition](/source/electronic_transition) into the vacancy and the [ionization energy](/source/ionization_energy) for the [electron shell](/source/electron_shell) from which the Auger electron was ejected. These energy levels depend on the type of atom and the chemical environment in which the atom was located.

[Auger electron spectroscopy](/source/Auger_electron_spectroscopy) involves the emission of Auger electrons by bombarding a sample with either [X-ray](/source/X-ray)s or energetic electrons and measures the intensity of Auger electrons that result as a function of the Auger electron energy. The resulting spectra can be used to determine the identity of the emitting atoms and some information about their environment.

[Auger recombination](/source/Carrier_generation_and_recombination) is a similar Auger effect which occurs in [semiconductor](/source/semiconductor)s. An electron and [electron hole](/source/electron_hole) (electron-hole pair) can recombine, giving up their energy to an electron in the [conduction band](/source/conduction_band), increasing its energy. The reverse effect is known as [impact ionization](/source/impact_ionization).

The Auger effect can impact biological molecules such as DNA. Following the K-shell ionization of the component atoms of DNA, Auger electrons are ejected, leading to damage to its sugar-phosphate backbone.<ref>{{Cite journal| doi = 10.1080/09553002.2017.1312670| issn = 0955-3002| volume = 93| issue = 8| pages = 743–756| last1 = Yokoya| first1 = Akinari| last2 = Ito| first2 = Takashi| title = Photon-induced Auger effect in biological systems: a review| journal = International Journal of Radiation Biology| date = 2017-08-03| pmid = 28397587}}</ref>

==Discovery==
The Auger emission process was observed and published in 1922 by [Lise Meitner](/source/Lise_Meitner),<ref>{{cite journal|doi=10.1007/BF01326962|author=L. Meitner|title=Über die Entstehung der β-Strahl-Spektren radioaktiver Substanzen|journal=Z. Phys. |volume=9|issue=1|year=1922|pages=131–144|bibcode= 1922ZPhy....9..131M|s2cid=121637546}}</ref> an Austrian-Swedish physicist, as a side effect in her competitive search for the nuclear beta electrons with the British physicist [Charles Drummond Ellis](/source/Charles_Drummond_Ellis).

The French physicist [Pierre Victor Auger](/source/Pierre_Victor_Auger) independently discovered it in 1923<ref>P. Auger: [http://gallica.bnf.fr/ark:/12148/bpt6k3130n.image.f187.langFR Sur les rayons β secondaires produits dans un gaz par des rayons X], C.R.A.S. 177 (1923) 169–171.</ref> upon analysis of a Wilson [cloud chamber](/source/cloud_chamber) experiment and it became the central part of his PhD work.<ref>{{cite journal|doi=10.3139/146.110163|title=Pierre Auger – Lise Meitner: Comparative contributions to the Auger effect|year=2009|last1=Duparc|first1=Olivier Hardouin|journal=International Journal of Materials Research |volume=100|issue=9|pages=1162–1166|bibcode=2009IJMR..100.1162H |s2cid=229164774 }}</ref> High-energy X-rays were applied to ionize gas particles and observe [photoelectric](/source/photoelectric) electrons. The observation of electron tracks that were independent of the frequency of the incident photon suggested a mechanism for electron ionization that was caused by an internal conversion of energy from a radiationless transition. Further investigation and theoretical work using elementary quantum mechanics and transition rate/transition probability calculations showed that the effect was a radiationless effect more than an internal conversion effect.<ref>{{Cite book |last=Burhop |first=E. H. S |url=https://archive.org/details/augereffectother0000ehsb/mode/2up |title=The Auger effect and other radiationless transitions (Cambridge monographs on physics) |date=1952-01-01 |publisher=University Press}}</ref><ref>{{Cite book |last=Chattarji |first=Dipankar |url=https://archive.org/details/theoryofaugertra0000chat |title=The theory of auger transitions |date=1976 |publisher=London; New York: Academic Press |isbn=978-0-12-169850-8}}</ref>

==See also==
*[Auger therapy](/source/Auger_therapy)
*[Charge carrier generation and recombination](/source/Carrier_generation_and_recombination)
*[Characteristic X-ray](/source/Characteristic_X-ray)
*[Coster–Kronig transition](/source/Coster%E2%80%93Kronig_transition)
*[Electron capture](/source/Electron_capture)
*[Radiative Auger effect](/source/Radiative_Auger_effect)

==References==
{{Reflist|30em}}

{{X-ray science}}{{Electron microscopy}}
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Category:Atomic physics
Category:Foundational quantum physics
Category:Electron spectroscopy

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Adapted from the Wikipedia article [Auger effect](https://en.wikipedia.org/wiki/Auger_effect) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Auger_effect?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.